Authorities say a woman was struck and killed on Interstate 15 by a passing vehicle after she exited the vehicle in which she was riding.
    
Montana Highway Patrol Capt. Gary Becker says the woman was hit Tuesday evening by a northbound vehicle that did not stop.
    
Becker did not know the identity of the woman. It was not immediately clear why she left the vehicle, where there was another person.
    
The northbound lanes south of Butte near the Buxton exit were closed that night while investigators gathered evidence. The closure backed up traffic for miles.